Electrostatography is best exemplified by the process of xerography as first described in U.S. Pat. No. 2,297,691 to C. F. Carlson. In this process, the photoconductor is first provided with a uniform electrostatic charge over its surface and is then exposed to imagewise activating electromagnetic radiation which selectively dissipates the charge in illuminated areas of the photoconductor while the charge in the non-illuminated areas is retained thereby forming a latent electrostatic image. This latent electrostatic image is then developed or made visible by the deposition of finely-divided electroscopic marking particles referred to in the art as “toner”. The toner will normally be attracted to those areas of the layer which retain a charge, thereby forming a toner image corresponding to the latent electrostatic image. This powder image may then be transferred to a support surface such as paper. The transferred image may subsequently be permanently affixed to the support by heat fusing. Instead of forming a latent image by uniformly charging the photoconductive layer and then exposing the layer to a light and shadow image, a latent image may be formed by charging an insulating or photoconductive insulating member in image configuration. The powder image may be fixed to the imaging member if elimination of the powder image transfer step is desired.
Several methods are known for applying an electrostatic charge to the photosensitive member such as the use of electron-emitting pins, an electron-emitting grid, single corona-charging structures and multiple dicorotron wire assemblies. In recent development of high speed xerographic reproduction machines where copiers can produce at a rate of or in excess of three thousand copies per hour, the need for several reliable dicorotron wire assemblies in order to utilize the full capabilities of the reproduction system is required. Also, with the advent of color copiers where several corona-charging stations are needed, the requirement for dependable dicorotron wire assemblies for depositing an electrostatic charge is essential.
Generally, in electrostatographic or electrostatic copy processes, a number of corotrons or dicorotrons are used at various stations around the photoreceptor. For example, the dicorotrons are used at the station that places a uniform charge on the photoreceptor, at a transfer station, at a cleaning station, etc. In today's high speed copiers, it is important that all corotrons (or dicorotrons) are in perfect working order since corotron malfunction can easily render the entire copying process useless. Some high speed copiers, including color copiers, use several dicorotron units, as many as sixteen corotron or dicorotron units are used. Maintaining each corotron unit in perfect working order is essential to the proper functioning of these complex fast color copiers. It is common to use one or several corona-generating device(s) (“corotron” or “dicorotron”) for depositing the electrostatic at the above-noted stations. Generally, the structure of a dicorotron uses a thin, glass-coated wire mounted between two insulating anchors or end blocks called “insulator barriers”, which support the wire in a spring-tensioned manner in a singular plane. These anchors are installed between flexible grippers, holders or clamps or anchor inserts that maintain the insulators in place. These insulator inserts are fixed at two opposite ends of a U-shaped dicorotron “housing” or “shells” or “shield”. The wire or corona-generating electrode is typically a highly conductive elongated wire situated in close proximity to the photoconductive surface to be charged. Often the corona discharge electrode is coated with a dielectric material such as glass. Glass coating improves charging uniformity throughout the electrode's life. Since the wire electrode is comprised of a thin outer glass brittle coating, it may be easily damaged. Some handling or cleaning of this electrode often results in fracture of the glass coating, which could cut or injure the user. While cleaning sometimes corrects problems in this corona electrode, it is sometimes necessary to replace the wire due to degradation in the corona performance or even in breakage of the electrode which could occur during the cleaning.
Manual handling of the glass-coated wire is not recommended nor is the use of prying tools, such as screw drivers or rigid prying objects. Extreme care needs to be observed in changing the corona electrodes or wires. As above noted, because of the large number of dicorotrons or wires needed in some copiers, malfunctioning of these wires presents a formidable problem in today's complex copiers.
Another important consideration is the high costs of dicorotron assemblies. The most expensive major component in the dicorotron assembly is the housing or U-shaped shield which houses the wire assembly and the wire anchors usually called insulators. The least expensive major component in the dicorotron assembly is the wire electrode. It makes sense, therefore, for the faulty wire assembly to be removed and replaced rather than the expensive entire dicorotron unit or assembly made up of the wire assembly and U-shaped housing.
There are some systems used to remove and replace wire assemblies from the U-shaped housing, such as the method disclosed in U.S. Pat. No. 5,449,906 (Osbourne). In this prior art system, the U-shaped housing has apertures on its end portions adjacent to the electrode anchors or insulators. A prying tool is then inserted into this aperture to pry or dislodge the two end anchors from their original position thereby removing the two insulators or anchors and the attached wire electrode. A tool for replacing the removed wire assembly in Osbourne's process includes a plurality of replacement electrodes mounted on a rigid support frame. Replacement is accomplished by pressing this support frame containing a plurality of corona-generating wire assemblies against the empty U-shaped housing (where old wire has been removed) and thereby replacing the removed wire electrode with a new wire electrode. This prior art process requires prying or dislodging the old wire through an aperture and replacing the old wire with a mounting system where a plurality of corona-generating electrode assemblies are removably mounted in a configuration matching that of the original configuration.